Ruellia britoniana

Plant type: evergreen perennial
Height: 3-5 feet
Cultural Requirements: pinch back after flowering, otherwise fairly adaptable.
Leaves: opposite, lanceolate leaves
Disease and Insects: none
Hardiness: zones 8-10
spacing: 15-18 inches

http://www.floridafriendlyplants.com/DatabaseImages/MexicanPetuniaPurpleShowers.jpg